Many airplanes today use capacitive based fuel quantity indicating systems, in which fuel probes include two concentric tubes that act as capacitors. Metal wires for the probes are inserted inside a fuel tank, and redundant supports are provided for the wiring, which increases an overall weight of the system, and increases a manufacturing time of the system.
In operation, as the probes are submerged in fuel in the fuel tank, a dielectric changes a capacitive output of the probes. The outputs of the probe are transmitted to a processing unit to determine a total amount of fuel in the fuel tank.
Other types of probes include ultra-sonic probes instead of capacitive probes inserted inside the fuel tank. The ultra-sonic probes are tubes and a top of the probes send an ultra-sonic signal to a bottom of the probes. The way the signal propagates through the medium, whether fuel or air, in combination with whether the signal contacts a fuel surface determines a fuel height in the fuel tank. Again, this type of quantity indicating systems requires metal wires in the fuel tank and redundant supports, which increases a system weight and manufacturing time.
What is needed is a fuel indicating system that provides an electromagnetic interference (EMI) safe system requiring no metal in the fuel tank, which eliminates metal wires in the fuel tank and a need for redundant supports as well as decreases system weight and manufacturing time.